Lithography processes are used in the manufacture of a variety of devices having one or more layers with micro-scale or nano-scale features. The current technology is challenged to meet the needs of high resolution (e.g. sub-50 nm feature sizes) and large area patterning (e.g. on substrates greater than 100 mm diameter).
Molecular transfer lithography (M×L) is one technique that can obtain the needed high resolution. Patterning of features is performed using dissolvable templates. For example, U.S. Pat. Nos. 6,849,558; 7,125,639; 7,345,002 and 7,981,814; and U.S. Patent Application Publication No. 2011/0058150 describe templates and a patterning procedure in which a material is transferred from a template to a substrate by adhesion, and then the template's polyvinyl alcohol (PVA) backing is dissolved in water. There are many possible types of transferred materials as the basic requirement is that the material coatings have minimal interaction with the PVA template. Among the types of materials that can be transferred with PVA templates include a polymer film, such as one with etch-resistant properties from which a pattern can subsequently be etched into the substrate, and vapor phase deposited films that have end-use properties such as a metal or dielectric layers.
M×L templates are themselves formed from a master that defines a target pattern to be replicated. However, a large area master is needed to create large area templates. At present, the areas that can be patterned by an optical photolithography scheme to create an original master for M×L template replication is limited to approximately 300 mm wafer diameter resulting in an approximately 200 mm square, and even smaller for original masters created by e-beam or other kinds of lithography. In order to create larger masters, multiple originals must be combined in some fashion. The most straightforward method involves simply tiling several original masters together, but can leave gaps or seam lines in the configuration at tile boundaries. Also, any difference in height between adjacent masters can cause defects in the pattern transferred to the new larger area master.
In U.S. Pat. No. 7,547,398 to Schmid et al., a self-aligned process for fabricating imprint templates is described which enables co-planarization of structures (e.g., micro-lenses) that are created in multiple independent etch steps with different portions unmasked. Co-planarization is needed when the various etches expose patterns to particular etching conditions, so that the various structures may exist at different planes or elevations relative to the template surface. Accordingly, “higher” structures must then be exposed to anisotropic etching to reduce their overall elevation while preserving the structural topography. There is no indication of patterning of high resolution features over large areas, nor any indication of how the technique might be used to avoid forming any gaps or seams between adjacent protected resist fields or unmasked aperture portions. As described it appears that it would suffer the same seam formation problem at boundaries as other tiling techniques, with an improvement from performing a subsequent an isotropic etch to obtain co-planarization.